1. Technical Field
The present disclosure relates to method of forming a polysilicon resistor during a replacement metal gate process, and a semiconductor device having the polysilicon resistor.
2. Discussion of the Related Art
Metal-oxide-semiconductor (MOS) transistors using polysilicon gate electrodes are known. Polysilicon material is able to tolerate high temperature processing better than most metals, so that polysilicon can be annealed at high temperatures along with source and drain regions. In addition, polysilicon blocks ion implantation of doped atoms into a channel region, facilitating the formation of self-aligned source and drain structures after gate patterning is completed.
The high resistivities of polysilicon materials, as compared to most metal materials result in polysilicon gate electrodes that operate at much slower speeds than gates made of metallic materials. One way of compensating for the higher resistance of polysilicon materials is to perform extensive silicide processing on the polysilicon materials so that the speed of operation of the polysilicon materials is increased to acceptable levels.
Another way of compensating for the higher resistance polysilicon materials is to replace a polysilicon gate device with a metal gate device. This replacement can be done with a replacement metal gate (RMG) process, wherein the higher temperature processing is performed while the polysilicon is present in the substrate, and after such processing, the polysilicon is removed and replaced with metal to form the replacement metal gate. More specifically, a device with a disposable polysilicon gate is processed, and the disposable gate and dielectrics are etched away, exposing an original gate oxide. The disposable polysilicon gate is then replaced by a metal gate having lower resistivity than the polysilicon material.
In known RMG processes, polysilicon is also removed from the areas forming resistors on the substrate, and replaced with metallic materials. As a result, the high resistive properties of polysilicon are not utilized for resistors on a substrate in which RMG processing has been performed.
Accordingly, there exists a need for a process in which polysilicon remains in the portions of a substrate forming the resistors so that polysilicon resistors can be formed even though an RMG process has been performed on the substrate.